1. Technical Field
The present invention pertains to pressurized infusion and temperature control systems for infused liquids, such as the type disclosed in U.S. patent application Ser. No. 09/380,507, entitled “Method and Apparatus for Pressure Infusion and Temperature Control of Infused Liquids” and filed Apr. 24, 2000, the disclosure of which is incorporated herein by reference in its entirety. In particular, the present invention is directed toward a system that controls the flow rate and temperature of a fluid within a flexible bag or container during infusion of the fluid from the container to a patient.
2. Discussion of Related Art
Intravenous (IV) fluids are typically infused into a patient utilizing a flexible bag or container filled with IV fluid and a fluid line to convey the IV fluid from the bag to the patient. The fluids are generally delivered from the container to the patient via gravitational forces and/or applied pressure. Typically, applied pressure is employed to control the infusion rate of fluid from the bag to the patient.
The related art provides several devices for regulating pressure applied to an IV fluid bag to control the infusion rate of fluid from the bag to a patient. For example, U.S. Pat. No. 4,090,514 (Hinck et al.) discloses a pressure infusion device including a bladder as part of the cuff in which a fluid filled plastic bag is encased. The bladder surrounds at least eighty percent of the plastic bag, and, upon fluid being pumped into the bladder, the fluid in the plastic bag is infused under pressure to a patient.
U.S. Pat. No. 4,551,136 (Mandl) discloses a pressure infusor for introduction of fluids into the human body. Two sheets of polyurethane overlie each other and are continuously sealed to form an air inflatable bladder. A strip of polyurethane projects from one vertical margin of the bladder to wrap completely around the liquid filled bag. A narrow elongated strap essentially attached to one margin of the infusor is long enough to wrap completely about the infusor with the bag enclosed. Velcro strips are secured to the strap to enable the strap to be fastened upon itself.
U.S. Pat. Nos. 5,308,335, 5,433,704, 5,584,811, 5,743,878 and Re. No. 35,501 (Ross et al.) disclose an infusion pump for infusion of a medical treatment fluid intravenously into a patient. The pump includes a collapsible treatment fluid bag juxtaposed with an inflatable drive fluid bladder confined between a pair of opposing containment members which cause the bladder to impinge against the bag as the bladder is inflated. A drive fluid pump controllably inflates the bladder, thereby displacing treatment fluid from the bag into an outlet tube affixed thereto which conveys the treatment fluid to the patient where it is received intravenously. The treatment fluid flow rate through the tube is controlled by increasing or decreasing the drive fluid pump output and consequently the pressure in the bladder in response to a pressure sensor in fluid communication with the bladder. In one embodiment, a first containment member is a rigid platen, while a second containment member is a flexible, yet inelastic, sheet loosely attached to the platen at opposite sides to form a sling. The bladder is positioned within the sling, while a fluid bag is slid into the sling in abutment with the bladder.
U.S. Pat. No. 5,681,284 (Herskowitz) discloses an infusion pump for infusion of solutions from IV bags through tubing to patients. The pump includes a housing having a compartment which receives an IV bag in a solution-dispensing position. The bag is placed over a bladder within the compartment, and the bladder is expanded by a pressurized fluid to apply a force against the bag to collapse the bag and infuse solution through the tubing. A pump in the housing pumps a fluid into the bladder in accordance with a control circuit. A pressure sensor indirectly senses pressure of fluid in the bladder through a pressure pad that contacts the bladder wall. The control circuit generates a pressure signal responsive to movement of the pressure pad for operating a valve which directs fluid between the pump and bladder.
The related art devices described above suffer from several disadvantages. In particular, the devices do not provide any control mechanism for maintaining the temperature of fluid flowing from the IV bag within a particular temperature range. This is of vital importance during infusion procedures in order to eliminate any potential for thermal shock and injury to the patient when the fluid enters the patient's body. In addition, the manual pressurization feature of the Hinck et al. and Mandl devices generally requires constant monitoring and manipulation of the devices by an operator in order to continuously maintain a desired fluid flow rate during infusion.
The related art has attempted to overcome the aforementioned problems by providing systems employing controlled pressure in combination with temperature control of IV fluid. For example, U.S. Pat. No. 5,125,900 (Teves) discloses a device for heating and pressurizing fluid filled containers. The device wraps around a flexible bag containing fluid to warm the fluid and to pressurize the bag so that warm fluid flows from the bag at a rate dependent upon the amount of pressure applied to the bag. The device includes a heating element that may be set at a preselected temperature and an inflatable bladder that may be inflated to a preselected pressure. The bladder is inflated manually utilizing a bulb.
U.S. Pat. No. 4,430,078 (Sprague) discloses a portable blood infusion pump designed to be employed in combination with a blood bag. The blood bag is located within a storage chamber that includes an inflatable bladder. Pressurized fluid is conducted within the inflatable bladder to press against the blood bag to enable discharge of the blood from the blood bag through a discharge conduit assembly. A container containing a supply of the pressurized fluid is mounted within the pump housing and is connected to the inflatable bladder. A pressure regulator is disposed in the housing to permit variance of pressure applied by the bladder against the blood bag in response to user manipulation of a knob. The pressure level applied by the bladder to the blood bag may be preset by a user via the knob while the regulator maintains the pressure level and automatically provides additional gas to the bladder in response to decreasing quantities of blood within the blood bag. An electrical heater apparatus may be included within the device to provide heat energy to the blood bag so as to warm the blood prior to being infused into a patient.
U.S. Pat. Nos. 5,879,329 and 5,989,238 (Ginsburg) disclose a system for infusing a fluid into a patient. The system includes a fluid reservoir and a temperature altering device in close proximity thereto. The temperature altering device is employed to heat or cool the fluid to a desired temperature. A positive pressure device in the form of a bladder and pressure source may be provided to place the reservoir under positive pressure while at the desired temperature. The pressure source maybe connected to a process or to control the total rate and volume of fluid introduced into the bladder, thereby controlling the rate and volume of fluid leaving the reservoir. A transfer member is further provided to transfer at least some of the fluid into the patient while at the desired temperature. In addition, the system may be portable for utilization in field applications.
U.S. Pat. No. 5,733,263 (Wheatman) discloses an apparatus for heating fluid contained in one or more bags and delivering the fluid from at least one bag to a surgical patient. The apparatus includes a housing to enclose at least one bag containing fluid and having a door positioned to provide access to the housing interior. The apparatus further includes an inflatable bladder mounted in the housing interior and connected to a source of pressurized fluid for inflation. The inflatable bladder exerts force against at least one bag mounted within the housing. A regulator permits regulation of gas pressure to the bladder in response to user manipulation of a housing regulator knob. In addition, the apparatus includes a heater mounted adjacent the housing door in heat transfer relationship with the fluid and at least one bag.
The related art devices described above providing both pressurized infusion and IV fluid temperature control suffer from several disadvantages. In particular, the Teves device requires constant monitoring and manipulation by an operator to maintain a desired flow rate of IV fluid from a bag to a patient. Further, the Teves device does not completely enclose a fluid bag within the device, thereby enabling skewed or non-uniform heating of IV fluid within the bag. Similarly, the Wheatman apparatus employs a heating element assembly located on the housing door that provides heat to one surface of the IV bag. These types of heating typically produce “hot” and/or “cold” spots within the IV fluid that may cause patients to receive the fluid at inappropriate temperatures, thereby risking injury to those patients.
In addition, the Sprague, Wheatman and Ginsburg devices typically house an IV fluid bag within a housing. Thus, these devices do not permit easy access and/or viewing of the bag during infusion. This typically requires medical personnel to repeatedly access the housing interior to monitor the bag (e.g., to determine the amount of fluid remaining within the bag and whether or not the bag needs to be replaced with a new bag) and/or increases the amount of time needed to replace an existing depleted or problematic bag with a new bag. The increased time needed to replace a bag may cause serious adverse conditions for a patient, especially during critical medical situations.